python: provide full typing for the REST client(s)

[multani]

This is a prototype to showcase the typing on the lower generated module, rest.py.

The goal with fully typing this module would be to then help build correct typing information on top of it.
This may also help in case we want to refactor the content of this module, and/or replacing it by another HTTP library.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (upcoming 7.1.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[robertschweizer]

BaseHTTPResponse is only introduced in urllib3 version 2.

Best use HTTPResponse. For me, dropping urllib3 version 1 support would be a problem, because boto3/botocore does not support it yet (boto/botocore#2926).

[multani]

Will revisit once #16802 has been merged.